Folding is described as the folding over of edge sections of molded parts, blanks or covers provided for the molded parts or blanks, such as shoe parts, suitcase handles, photo albums, appointment books, diaries, eyeglass cases, binders or the like. The folded-over edge section is pressed during the folding operation onto the base area of the molded part or blank and glued to it or bonded to it using compression means. Usually the folding is performed on essentially flat workpieces, for example those made of leather, artificial leather, plastic, or the like. However, the principle can also be generally applied to any desired molded parts where edge sections are bent over.
The edge sections to be bent over are generally quite narrow, requiring precise work. Therefore, the folding operation is often done manually, particularly when round corners render it relatively difficult. Folding dies are already known, however, in which the folding operation and the compressing of the folded-over edge sections are capable of being carried out automatically. A known folding die comprises a base plate, upon which a sizing plate, supported by springs, is mounted so as to be vertically movable. In the sizing plate, a cut-out is formed, into which a pressure plate is inserted that is likewise movably supported by springs on the base plate, and whose dimensions correspond exactly to the dimensions of the finished molded part or blank. In an upper die, a folding plate is movably supported by springs on a fixing plate. In the folding plate, a cut-out is formed, into which is inserted a pressure plate that is likewise movably supported by springs on the fixing plate. A circumferential projection is formed around the cut-out in the folding plate. For the folding operation, a molded part or blank is placed on the pressure plate, the edge sections of the molded part or blank to be folded over projecting on the side out over the pressure plate. The proper arrangement of the molded part or blank on the pressure plate is guaranteed by guide strips mounted on the sizing plate. At this point, the upper die is moved down, so that the pressure plate is pressed downward by the pressure plate projecting out over the folding plate and is lowered through the cut-out in the sizing plate. The edge sections of the molded part or blank projecting out over the folding plate are bent over at the edge of the cut out in the form plate when the pressure plate is pressed down, so that they essentially point up perpendicularly along the circumferential wall of the cut-out. When the top die is pressed down further, the edge sections of the molded part or blank pointing upwards are bent over by the projection formed around the cut-out in the folding plate to the inside on to the base area of the molded part or blank and pressed by an annular rim stamp, which is mounted on the fixing plate and is arranged between the rim of the cut-out in the folding plate and the pressure plate. Since the pressure plate of the top die that is pressing the pressure plate down is not able to engage with the entire surface of the pressure plate due to the rim to be left free for the edge section to be bent over, it is precisely in those edge areas of the pressure plate essential to the folding operation that a well-defined guidance of the bent-over edge sections is not possible, so that uneven folding can result. Another significant disadvantage of the known folding dies is that the pressure plate, the sizing plate, the folding plate, and the pressure plate of the top die must be precisely adjusted to one another for each molded part, so that the change of a shape or changing the dimensions of the object to be folded over requires replacement of the entire folding die. Since, as described above, the folding operation is applied to a plurality of different objects of greatly differing sizes, considerable costs are entailed by the many required sets of dies. Moreover, in the case of the known folding tool, four spring steps of the base plate, the sizing plate, the folding plate, and of the pressure stamp must be harmonized to one another, which is also very costly.